Compact high efficiency electrostatic precipitator for droplet aerosol collection

ABSTRACT

An electrostatic precipitator has a high voltage electrode including multiple wire segments that are positioned within a surrounding electrically conductive porous media having a central axis and wherein the electrode assembly extends along the central axis. The electrode assembly has a plurality of wire lengths positioned to extend in a direction along the longitudinal axis of the porous media, and the wire segments being arranged to have a substantially longer total length than the length of extension along the longitudinal axis. An aerosol containing droplets is passed into the interior of the porous media, and across the electrode, which is charged with a high voltage. The porous media is at a substantially lower or different voltage from the high voltage electrodes. Flow of the aerosol containing particles charged by the electrode passes through the porous media to the outlet and the charged particles are precipitated by the porous media. Electrostatic shields are provided around high voltage insulators to reduce the likelihood of contamination of the insulators, which causes unsatisfactory current leakage.

BACKGROUND OF THE INVENTION

[0001] This invention relates to droplet aerosol collection byelectrostatic precipitation, and methods that improve efficiency forparticle collection. The improvements include one or more of the use ofmultiple, thin wire discharge electrodes; the use of a conductive porousmedium as a collecting surface; the use of high voltage electrostaticshield to prevent particle deposition on the insulator for thecomponents; and the use of heated insulator to prevent vaporcondensation and particle deposition by thermophoresis.

[0002] Electrostatic precipitation is one of the most widely usedmethods for removing suspended particulate matter from a gas for gascleaning or air pollution control. In comparison with other particulatecollecting devices, such as cyclones, wet scrubbers, filters, and thelike, an electrostatic precipitator has the advantage of low pressuredrop, high collection efficiency and requiring relatively small amountsof electrical power for its operation. The low pressure drop of theelectrostatic precipitator makes the device most advantageous with largevolumetric flow rates of the gas flow needing treatment. Electrostaticprecipitation have been used extensively for large scale industrialapplications, such as removing fly ash from power plants, controllingparticulate emission from smelters, steel and cement making and othersimilar industries, and general purpose air cleaning for buildingventilation. A typical electrostatic precipitator may operate at severalhundred cubic feet per minute of flow in small systems, to severalmillion cubic feet per minute for large industrial installations.

[0003] The first laboratory demonstration of electrostatic precipitationwas made by Hohifeld in 1824, according to credible sources. The firstU.S. patent on electrostatic precipitation was issued to Walker in 1886as U.S. Pat. No. 342,548. Numerous other electrostatic precipitatorpatents have been issued over the years. Those considered the mostsignificant include U.S. Pat. No. 895,729 to Cottrell on the use ofrectified alternating current for electrostatic precipitation, and theinvention of the liquid film precipitator by Bums as shown in U.S. Pat.No. 1,298,088; the fine wire electrode and two-stage precipitationsystem of Schmidt, U.S. Pat. No. 1,329,285; the low-ozone air-cleaningprecipitator of Penney U.S. Pat. No. 2,000,654; and pulse energizing ofprecipitators disclosed in U.S. Pat. No. 2,509,548 to White, amongothers.

[0004] The fundamental design of the electrostatic precipitator hasremained relatively unchanged over the years. In its simplest form for asingle stage precipitator, a high voltage electrode is placed in thecenter of a grounded tube. A high DC voltage on the small diametercenter electrode causes a corona discharge to develop between theelectrode and the interior surface of the tube. As the gas containingsuspended particles flows between the electrode and the wall of thetube, the particles are electrically charged by the corona ions. Thecharged particles are then precipitated electrostatically by theelectric field onto the interior surface of the collecting tube.

[0005] One disadvantage of the electrostatic precipitator is itsrelatively large physical size. According to Deutsch (W. Deutsch, Ann.der Physik, Volume 68, p. 335, 1922), the basic equation governing theoperation of the electrostatic precipitator is:

η=1−e ^(−A w/Q)

[0006] The Deutsch equation relates the precipitator collectionefficiency, η, to the collecting area of the precipitator, A, thevolumetric flow rate, Q, through the precipitator, and the electricalmigration velocity, w, of the particles. e is the constant, 2.718, thebase of natural logarithms. For a specific application, the collectingarea of the precipitator, A, is determined when the required volumetricgas flow rate, Q, is known. To reduce the overall physical size of theprecipitator, closely spaced precipitating plates can be used. However,there is a limit on this approach to reducing physical size. When theresulting physical size of the precipitator is still too large for theapplication, an electrostatic precipitator is then consideredunfeasible.

[0007] Several applications have developed in recent years where asignificant reduction in the overall physical size of the electrostaticprecipitator is needed. One application is the removal of the suspendedparticulate matter from the blowby gas from a Diesel engine. In Dieselengines, the high temperature, high pressure combustion gas in theengine cylinder has a tendency to leak past the piston rings into thecrankcase. This is usually referred to as the blowby gas. This blowbygas contains lubricating oil droplets from the lubricating oil filmsatomized by the high velocity blowby gas flowing from the high pressurecylinder into the crankcase. It also contains Diesel exhaustparticulates, which result from the incomplete combustion of the Dieselfuel in the engine cylinder. The amount of blowby gas is relativelysmall for new engines, but will increase over time as the engines age,and the piston rings no longer provides a good seal. This blowby gasusually has a flow rate of few cubic feet per minute to perhaps as highas 20 cfm for engines in good operating condition.

[0008] The Diesel blowby gas is currently being exhausted directly intothe atmosphere. In order to protect the environment, there is a need toremove suspended oil droplets and Diesel exhaust particulates in theblowby gas so that the blowby gas can be returned to the fresh airintake side of the Diesel engine for further combustion. This “blowbygas recirculation system” is practical only when the suspendedparticulate matter is removed to avoid contaminating the components andequipment located on the air intake side of the Diesel engine. One suchcomponent is the turbo charger or compressor used to supercharge theDiesel engine to increase its power output and efficiency.

[0009] For application in the blowby gas recirculation system, theelectrostatic precipitator must be compact and reliable. It is alsodesirable that the operating voltage of the precipitator be relativelylow so that very a high supply voltage is not needed.

[0010] Another application for an electrostatic precipitator that isreduced in size from existing precipitators is for removing suspendedoil and grease particles in the exhaust gas from commercial kitchens,including kitchens in fast-food, as well as conventional, restaurants.

[0011] A third application of an electrostatic precipitator of reducedsize is to remove cutting fluid droplets from the machine shopenvironment. During machining of metal parts, a cutting fluid is usuallydirected at the tool and the parts being machined to provide cooling aswell as lubrication. Some of this cutting fluid is aerosolized to formsmall droplets by the higher speed rotary cutting tool. This cuttingfluid aerosol presents a heath hazard to the workers and must befiltered to remove the suspended droplets. Conventional fibrous filtersare not suitable for this application, because the collected dropletstend to clog the filter and produce excessive pressure drop in a shorttime. The inherent advantage of the small compact physical size and theinherent flame arresting properties of the precipitator of the presentinvention makes it particularly suited for these applications.

[0012] It should be noted the term “compact size” is used here in arelative sense to indicate that the size of the precipitator designed onthe basis of this invention is smaller or more compact in comparisonwith electrostatic precipitators of a conventional design at the sameflow rate and at the same efficiency level. By necessity, as a dieselblowby particle collector, the electrostatic precipitator must besufficiently small to fit under the hood of a truck powered by a dieselengine. The overall volume of the collector must be no more than a fewliters, preferably below two liters. On the other hand, an electrostaticprecipitator designed for kitchen exhaust applications will need to beconsiderably larger because of the high flow rate of the exhaust gas tobe treated. Such a collector can also be called compact even though thecollector is several cubic feet in total volume so long as the collectorof the conventional design is even larger, perhaps by as much as 50 or100%.

SUMMARY OF THE INVENTION

[0013] The present invention is an electrostatic precipitator that hasimproved operating efficiency while being smaller in physical size thanexisting devices that handle similar flow rates. The present device usesmultiple electrical wire discharge electrodes which permit reducing thelength of the precipitator. An electrically conductive porous medium ispreferably used as the collecting surface. A further aspect of theinvention is an electrostatic shield used to reduce or prevent particledeposition on the insulators for high voltage components. A furtheraspect of the invention is use of heated electrodes which prevent vaporcondensation and also prevent particle deposition by thermophoresis.

[0014] All aspects of the invention cooperate to increase efficiency andreduce physical size for a given flow rate. These improvements have madeit possible to significantly reduce the overall physical size of theprecipitator. The small, compact physical size has in turn made itpractical to use electrostatic particle collection for the aboveapplications where small physical size is important. Treating dieselblowby exhaust to remove suspended oil droplets and particulate matterpermits the blowby exhaust gas to be discharged to the ambient withminimal amount of particulate air pollutant, or to be returned to theair intake side of the diesel engine for exhaust gas recirculation. Whenused to remove oil and grease particles contained in the exhaust ofcommercial kitchens the organic particulate matter will be removed.Another application is collecting droplet aerosols of cutting-fluid inmachine shops where sprayed liquids enter the atmosphere.

[0015] While the present invention was primarily developed forapplications such as those described above, the small compact size ofthe new precipitator makes the device suitable for a variety of otherapplications, even in those cases where small physical dimensions arenot a primary requirement.

[0016] For the purpose of this disclosure, Aerosol is defined as smallparticles suspended in a gas. The particles can be a solid, a liquid, ora mixture of both. The particle size can range from approximately 0.001μm to 100 μm, with 0.01 μm to 20 μm being the size range of the greatestinterest. For the present application, most of the mass of aerosolparticles to be collected is concentrated in the latter size range.Droplet aerosol is defined as an aerosol in which the suspendedparticles are primarily in a droplet form and having a spherical shape.However, the liquid droplets need not be a pure liquid, and may containsuspended solid particles within each droplet.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic cross sectional view of a compactelectrostatic precipitator made according to the, present invention;

[0018]FIG. 2 is a sectional view taken on horizontal line 2-2 in FIG. 1;

[0019]FIG. 3A is a schematic sectional view of a modified form of theelectrode support and high voltage shield used with the precipitator ofFIG. 1;

[0020]FIG. 3B is a further modified form of a electrode support and highvoltage shield used with the precipitator of FIG. 1;

[0021]FIG. 4 is a transverse sectional view of a precipitator madeaccording to the present invention but having a rectangularconfiguration;

[0022]FIG. 5 is a schematic representation of an ultrasonic generatorused for introducing aerosols into the electrostatic precipitator in thepresent invention;

[0023]FIG. 6 is a cross sectional view of a modified compactprecipitator using a different style of electrode assembly from thatshown in FIG. 1;

[0024]FIG. 7 is sectional view taken on line 7-7 in FIG. 6;

[0025]FIG. 8 is a sectional view of a still further modified form of aelectrostatic precipitator of the compact electrostatic precipitator ofthe present invention;

[0026]FIG. 9 is a sectional view taken on the line 9-9 in FIG. 8;

[0027]FIG. 10 is a schematic block diagram of a blowby gas recirculationsystem used in a diesel engine;

[0028]FIG. 10A is a modified recirculation system similar to that shownin FIG. 10;

[0029]FIG. 11 is a further modified block diagram of a blowby gasrecirculation system used in a diesel engine;

[0030]FIG. 12 is a block diagram similar to FIG. 11 with a controlledflow restrictor on the outlet of the intercooler;

[0031]FIG. 13 is a cross sectional view of a modified support for theelectrode wire;

[0032]FIG. 14 is a vertical sectional view of a further modified compactelectrostatic precipitator;

[0033]FIG. 15 is a sectional view taken on line 15-15 in FIG. 14;

[0034]FIG. 16 is a cross sectional view of a modified support for theelectrode wire as it would be taken along the line 15-15 of FIG. 14;

[0035]FIG. 17 is a cross sectional view of a modified support for theelectrode wire as would be taken along the line 17-17 of FIG. 14; and

[0036]FIG. 18 is a flat layout of a cylindrical electrode supportunrolled to a flat surface to reveal a modified pattern for theelectrode wire supported on the electrode surface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0037]FIG. 1 is a schematic cross sectional view of an electrostaticprecipitator 10 made according to the present invention. A housing 12has a discharging electrode assembly 14 to produce the corona discharge.The high voltage DC power supply 16 applies a high voltage (severalthousand volts), to the electrode assembly 14 on a wire surrounded by aninsulator bushing 18. The bushing 18 is surrounded by a high voltageshield 20, made of suitable conducting material.

[0038] An electric heater 22 is in contact with the insulator bushing 18to keep the insulator bushing at a sufficiently high temperature toprevent vapor condensation and particle deposition on the bushing 18.

[0039] Gas containing suspended droplets and other particulate matterfrom a source 23 is directed to flow through an inlet opening 24 of thehousing 12 and passes through a porous medium 26 in the inlet. Theporous medium 26 is a relatively inefficient droplet collector to keepout large contaminants, so that most of the droplets in the aerosol arecarried by the gas into the electrostatic electrode region or chamber 28above.

[0040] The input gas then flows around the electrode assembly 14 toexpose the droplet particles in the gas to the high electric fieldaround the electrode assembly. The discharge electrode assembly 14includes a central rigid support 30 for two support discs 32 and 34 onopposite ends of the central support. The upper disc 32 may be attachedto the insulator bushing 18 and thus support the discs 32 and 24 fromthe housing 12. A plurality of holes 35 (see FIG. 2) are formed in eachdisc 32 and 34 and a fine metal wire, 36 is strung between them. Thesectional view FIG. 2, through the compact electrostatic precipitatorelectrode 14 shows there are eight holes in each of the support discs. Afine metal wire 36 is threaded through the holes to form eight straight,parallel discharge electrodes 36. By way of example, if the distancebetween the two support discs is 8 inches, the fine wire electrode 36extending between them will each be 8 inches in length for a totaldischarge electrode length of 64 inches. More holes can be used in thesupport discs 32 and 34 to create more discharge electrodes, or fewerholes can be used if less length of the discharge electrodes is needed.With the above mentioned distance of 8 inches between the support disks,an electrode circle diameter of 3 inches, the diameter of the housing 12is approximately 5 inches, and its length, approximately 10 inches.Using the conventional design of a single discharge electrode in thecenter of a tube, the total length of the electrostatic precipitator ismore than 64 inches. The advantage of the present electrode design inreducing the size of the precipitator and making it compact over theconventional design thus becomes obvious.

[0041] The gas (aerosol) flows around the wires 36 and ions are producedin the corona discharge. The ions collide with the droplets to cause thedroplets to be charged. The charged droplets are then carried by the gasflow through an electrically conducting, grounded porous medium 40 asthe gas flows to an outlet 42. The droplets are collected byelectrostatic precipitation onto the grounded collecting elements in themedium.

[0042] The clean gas then flows out of the annular space 41 between theporous medium 40 and the outer housing 12 to the outlet 42. Thecollected oil droplets flow down the inside surface of the porous medium40 as a thin film which is returned by gravity to an oil reservoir orsump 44.

[0043] As shown in FIG. 1, all parts of the system are grounded exceptfor the high voltage electrode assembly and the high voltage shield 20.

[0044] Using a thin wire of a uniform diameter in the above electrodearrangement, and in other embodiments disclosed, it is important to keepthe distance between each wire segment and the adjacent collectorelectrode the same for all the wire segments on the support structure.By keeping the distance uniform and using the same high voltagepotential on all the wire segments, a uniform corona discharge can bemaintained. This will insure that all particles flowing through thedevice will be charged uniformly and to the same maximum possible extentto insure high collection efficiency for the device.

[0045] In designing an electrostatic precipitator using the aboveelectrode assembly, the spacing, S, between the wire segments must beara proper relationship to the distance, D, between the wire segment andthe adjacent collector electrode surface. (see FIG. 2). Too small aspacing, S, will cause the closely spaced wire segments to interferewith each other, thereby reducing the maximum current that can beobtained from each wire. Too large a spacing will cause some empty spotson the collector electrode surface to appear. Within these empty spots,there are no corona current flow. Particles flowing over these emptyspots will not encounter corona ions and thus remain uncharged. Fromexperience, it has been found that the ratio, S/D, must be kept betweenthe limits of 0.1 and 10, preferably between 0.3 and 3, for theelectrode assembly to function properly and avoid degradation inperformance.

[0046] For application in a Diesel blowby gas recirculation system, theinlet housing 24 is connected to an opening in the crankcase, which isrepresented at 23, and the collected oil film is also returned directlyto the crankcase. The outlet 42 can be open to the atmosphere to allowthe cleaned blowby gas to be discharged to the atmosphere, or the outlet42 can be connected to the intake of the Diesel engine for exhaust gasrecirculation.

[0047] The total discharge electrode length is greatly increased fromthat of the conventional precipitator with a single discharge electrodein the center of a tube. The corona current that can be maintainedbetween the discharge electrode and the collecting tube is generallyproportional to the total electrode length. The approach described heremakes it possible to greatly increase the electrode length and hence thetotal corona current, thereby increasing the efficiency for both dropletparticle charging and precipitation of the charged droplets orparticles. A laboratory prototype device has demonstrated thepracticality of this approach. As many as sixteen discharge electrodeshave been used leading to approximately a factor of sixteen increase intotal corona current in laboratory prototypes.

[0048] Another purpose of the electrode design shown is to allow thedischarge electrode to be circumferentially supported on a circle. Alarge diameter circle of the electrode length mounting will bring thedischarge electrodes (the wires) closer to the porous medium 40collecting surface, thereby reducing the voltage needed to maintain thecorona discharge between the electrode and the grounded porouscollecting surface. A lower operating voltage from existingprecipitators is desirable for the applications described above, toreduce the need for very high voltage insulation. When using a lowervoltage, the leakage current through the insulator bushing 18 can bereduced. Using a lower voltage also reduces the cost and complexity ofthe power supply 16, thus making the device more economical to produce.In the present device, voltages of between 5,000 to 10,000 volts aremost preferred, but voltages up to 20,000, volts DC can be used.

[0049] Using a circle of electrode lengths spaced from the center rodalso forces the gas flowing radially outward toward the porouscollecting surface to be exposed to the very high electric fieldsurrounding each discharge electrode. Generally, the electric fieldstrength according to Gauss's law tends to decrease with increasingdistance from the discharge electrode. The closely spaced wires formingthe discharge electrodes forces the gas to pass through the high fieldregion between the electrodes and to be exposed to the high electricfield around the wires. Each droplet or particle can thus be charged toa higher level than is possible with the conventional single lengthelectrode design, thereby gaining a higher electrical charge andallowing droplets to be more easily removed by electrostaticprecipitation.

[0050] Although a porous collector electrode 40 is shown in FIG. 1 asthe collector electrode, the basic design of the discharge electrodeassembly 14 works well also when the collector electrode is made of asolid conducting material, in which case the housing 12 itself can bethe collector. The oil droplets will be collected on the interiorsurface of the housing walls. The collected oil droplets will then flowdown the walls and be returned to the oil sump or the crankcase of thediesel engine, eliminating the porous collector electrode will make thedevice less efficient, but the overall size, the complexity, and thecost of the device will also be reduced.

[0051] The high-voltage insulator bushing 18, if unprotected, will beexposed to the suspended droplets or particles in the gas, as well asany condensable vapor which may be present. Over time, the accumulationof deposited and condensed material on the insulator will render itineffective. The insulator is heated by contact with the electricalheating element 22 to a high enough temperature to prevent vaporcondensation on the insulator bushing.

[0052] To prevent the precipitation of droplets or particles on theinsulator bushing surface, a conductive shroud or shield 20 surroundsthe insulator. This conductive shroud 20 is connected to the same highvoltage source as the discharge electrodes 36 so that a high electricfield is created in the region between the shroud and the nearbygrounded surfaces of the porous medium 40 or housing 12. The chargeddroplets or particles present in the gas will thus be precipitated ontothe grounded surfaces and not on the high voltage insulation bushing.

[0053] Design variations of conductive shroud 20 are shown in FIGS. 3Aand 3B. By using a small gap spacing between the bottom plate of theshield or shroud and the nearby grounded surface, a high electric fieldcan be created in this gap space to also precipitate droplets orparticles in the gas.

[0054] In FIG. 3A, the modified high voltage shield as indicated at 50,and as shown has a base plate 50A, and the surrounding wall SOB thatsurrounds the insulator bushing 18. The grounded housing 12 has a capportion 52 that comes up from a top wall 54 and defines an opening nearthe upper end of the insulator 18, as shown. The surrounding wall 50B isspaced from the wall over cap 52, and terminates short of the upper endwall of the cap. Thus there is a gap shown at 56 between the shield wall50B and the housing wall 52 around the insulator. The support shown at56 supports a top plate 32 of the electrode assembly. The centralsupport and the lower electrode plate 34 can be provided as before.

[0055] In FIG. 3B, the high voltage shield comprises a flat disc 60 thatis fixed to the lower end of the insulator bushing 18, and the insulatorbushing 18 in this case is also surrounded by a sleeve or cap 62 of thehousing, which is grounded.

[0056] The top wall 64 of the housing is spaced from the plate 60, toform a gap 66 between the housing wall 64, which is a top wall, and theplate 60 which is a shielding disc. The support 68 can be used forsupporting a top plate 32 of the electrode assembly as before.

[0057] Each of these forms of conductive shroud shows a gap between thehigh voltage shield or shroud and a portion of the grounded housing. Thegap is relatively narrow, and will provide for precipitation of chargedparticles that come near the high voltage shield, to the walls of thegrounded housing.

[0058] Creating a long pathway in the gap space as shown in FIGS. 3A and3B, the charged droplets or particles in the gas can be efficiencyprecipitated in the regions surrounding the insulator bushing 18 toprovide improved protection of the high voltage insulator fromparticulate contamination.

[0059] In spite of the efficient high voltage insulator shield design ofthis invention, there is the possibility that some droplets or particlesin the gas may remain uncharged. These uncharged particles will becapable of penetrating through the gap space 56 or 66 between the shroudand the nearby grounded surface to deposit on the insulator. Theprecipitation of these uncharged particles on the insulator can beprevented by utilizing the phenomena of thermophoresis. Thermophoresisrefers to the movement of aerosol particles in the direction of adecreasing temperature gradient due to the radiometric force acting onthe particles. For effective thermophoretic motion of the particles toprevent particle precipitation on the insulator the insulator must heheld at a sufficiently high temperature. The insulator temperature mustbe 10° C. or more than the surrounding gas temperature. In contrast, toprevent vapor condensation, the insulator only needs to be held abovethe dew point of the condensable species in the gas. Usually at least afew degree C above the gas temperature would be sufficient

[0060] To be effective, the porous medium 40 must be made of aconductive material, usually metal. It can be made of a perforatedmetal, a porous, sintered metal, one or more layers of wire meshmaterial rolled into the desired cylindrical shape, a pad of metal fiberor wires formed into a cylinder, and similar configurations. As the gasflows into the porous medium, particles are brought to close proximityto the surface of the conducting elements in the medium, thus allowingthe charged particles to be effectively deposited onto the surface ofthe conducting elements of the porous medium. In comparison, in theconventional electrostatic precipitator using solid collectingelectrodes, such as a solid tube surrounding the center electrodes, thecharged particles must be precipitated by electrical force through thefluid boundary layer adjacent to the inner surface of the surroundingtube.

[0061] Depending on the gas flow velocity, the relatively stagnantboundary layers adjacent to the solid collecting surfaces may be acentimeter or more in thickness. The particles must be precipitatedthrough this centimeter thick stagnant gas layer to be deposited on thesurface. In comparison, using a porous collecting electrode, as shownhere, the gas is forced to flow between the closely spaced conductingelements in the porous medium, thereby greatly reducing the distance theparticles must travel to reach the collecting surface. This willincrease the efficiency of the precipitator and reduce the overallphysical size of the device.

[0062] Not all electrically conducting porous material can be used withthe compact electrostatic precipitator described in this invention. Inorder to handle the high gas flow rate per unit of collecting surfaceintended for this application, the porous material must not produceexcessive pressure drop at the required high gas flow. In addition, thecollected oil drops must drained off easily by gravity and not becollected in the porous medium to clog the medium or produce excessivehigh pressure drops. Depending on the structure of the porous medium,and the surface tension and viscosity of the liquid droplets beingcollected, the distance between the conducting elements of the porousmedium must be kept above a critical limit. Too small a distance willallow the collected droplets to form surface films bridging neighboringelements and block the flow. For the usual liquid such as lubricatingoils, the mean distance between the conductive elements in the mediummust be larger than about 5 microns, and preferably larger than 10 μm.The mean distance between the elements in a porous medium is alsoreferred to as the mean pore diameter which can be measured by acommercial poremeter. A mean pore diameter greater than 5 μm, preferablygreater than 10 μm, is generally necessary for the medium to worksuccessfully as the porous collecting electrode of the dropletcollecting precipitator described herein.

[0063] There are a number of devices using a porous medium to collectcharged particles. One such device is the electrically augmented bagfilter described by Penney in U.S. Pat. No. 3,910,779. In Penney'sdevice, the particles are charged in a corona charger. The chargedparticles are then carried by the gas flow through a fabric medium anddeposited on the surface of the fabric. The particles to be depositedmust be a dry solid material, so that the deposited particles on thefabric will form a porous cake. Since a cake will also form on thefabric in the absence of an electrical charge, electrostatics chargesare used by Penney to modify the property of this cake namely toincrease the pore size of the cake and reduce the pressure drop. Thetextile fabric used in a fabric filter is usually not electricallyconductive, so that it is not possible to maintain a corona dischargedirectly between the corona electrode and the fabric. A separate coronacharger is used upstream of the fabric filter to charge the particlesfor subsequent filtration by the fabric.

[0064] Another device using a porous filter media is what is usuallyreferred to as electrostatically enhanced fibrous filter such as thatdescribed by Carr in U.S. Pat. No. 3,999,964. A conventional fibrousfilter media made of glass, polymeric and other non-conducting fibers issandwiched between two sets of electrical grids. A potential differenceis established between the grids to create an electric field in themedium to enhance the efficiency of the medium for particle collectionby electrostatic attraction. The device is most effective when theparticles are electrically charged. If the particles are not charged, acorona ionizer can be used upstream of the filter to charge theparticles to increase the efficiency of the filter for particlecollection.

[0065] A further version of the electrostatically enhanced fibrousfilter is that of Argo et al in U.S. Pat. No. 4,222,748. In Argo'sdevice, a corona charger is used upstream to charge the particles. Asthe charged particles are collected in the fiber bed, which is made of anon-conductive material, charge will build up in the bed to raise itselectrical potential. To prevent the continuous buildup of charge in thebed, the bed is continuously irrigated by water to make the bedconductive. Particles collected in the bed are also carried away by theflowing water.

[0066] The electrostatic precipitator of the present invention is veryefficient and can be made into a small compact size. For manyapplications, such as diesel blowby filtration, the cylindrical geometrywith a circular cross section is the most convenient. However, it is notnecessary that the cross section shape be a circle to take advantage ofmany of the features of this invention. Rectangular, elliptical, andother cross sectional shapes can be easily adapted to the design of anelectrostatic precipitator described by the method described in thepresent invention.

[0067]FIG. 4 represents a transverse sectional view through arectangular precipitator. The electrode assembly 72 including a pair ofspaced corona wire supports 74 (only one is shown) would be made asbefore with the two supports 74 spaced along a support rod 76 with wire77 forming electrodes extending between the supports. The wires 77 areshown in the cross over portions for threading through the holes. Aconductive porous medium collecting electrode 78, surrounds the highvoltage electrode assembly 72, and the porous medium, and the groundedouter housing 79 have a generally rectangular cross-sectional shape.

[0068] In designing such a rectangular precipitator, it is important tokeep the individual corona wire lengths between the support 74 atapproximately the same distance from the porous collecting electrode 78.This will insure that the corona discharge between the high voltagecorona wire 76 and the collecting electrode 78 will be uniform at thesame applied voltage on the wires. As before, the lateral distancebetween the wire lengths and the porous collecting electrode 78 can bereduced to lower the required operating voltage of the precipitator.

[0069] Although the precipitator described in this invention is intendedfor droplet aerosol collection, it can also be used to collect aerosolscontaining only dry solid particles. To prevent the build up of solidparticles in the porous collecting electrode which will cause pluggingof the pores, liquid droplets, usually water, can be added to theaerosol before it is introduced into the precipitator. FIG. 5 shows anultrasonic droplet generator 80 used in conjunction with anelectrostatic precipitator 82 for droplet addition. As aerosol flowsfrom source 84 through the ultrasonic generator 80, it picks up dropletsin the space 86 above an agitated liquid 88 produced by ultrasonicagitation using an ultrasonic transducer 89. The dry particulate matterwill be precipitated along with the added liquid droplets in theprecipitator 82 and be carried away by the liquid stream resulting fromthe collected droplets, thereby preventing the build up of dry solidmaterial on the collecting electrode in the precipitator. Other dropletgenerating devices, such as compressed air atomizer, bubblers, and thelike can also be used. The electrostatic precipitator can be made asshown in any of the forms disclosed

[0070] Because of the small droplet size and the large surface area ofthe droplets produced by ultrasonic agitation or a compressed airatomizer, the combined wet electrostatic precipitator and dropletgenerator described above will have excellent gas absorptive properties,and can be used as a combined gas and particle scrubber. The combinedgas and particle scrubber will have a variety of applications in airpollution control. For instance, in the semiconductor industry, theexhaust gas from the vacuum pump downstream of a semiconductor processequipment often contains both toxic gases as well as fine particulatematter. One such gas is fluorine, which is used at the end of a processcycle to clean the process chamber. Fluorine is very reactive to waterand will be efficiently scrubbed by water droplets in the combineddroplet generator and wet electrostatic precipitator. Similarly, variousacidic vapors such as hydrogen fluoride (HF) and hydrogen chloride (HCl)can be absorbed by water droplets or by an aqueous solution of KOH andother basic solutions. By combining a droplet generator with appropriatechemical scrubbing solutions and the wet electrostatic precipitator, ahighly efficient combined gas and particle scrubber can be obtained.

[0071]FIGS. 6 and 7 show a compact two-stage electrostatic precipitator98 in which an electrode assembly 100 including a short corona-dischargeelectrode 102 that is attached to a cylindrical precipitating electrode104, and both are held at the same high DC voltage from a voltage orpower source 106. The short corona-discharge electrode 102 has a pair ofspaced support discs 108 and 110 held together with a central support112. The discs support a fine wire 113 carrying a high voltage toproduce a corona-discharge. The cylindrical electrode 104 is a tubularcylinder with a conducting surface. This cylindrical electrode 104together with the surrounding porous metal media collector 114 form aprecipitating region in which the charged particles are precipitated.

[0072] In this two-stage design, the relatively short corona wirelengths 113A forming electrodes produce a corona discharge to charge thedroplets or particles moving past the corona-discharge electrode 102.The short length of electrode 102 reduces the corona output from thewires, hence the required current output from the power source 106 isreduced, in turn reducing its physical size, and cost. The design alsomakes it possible to vary the radius of the circle of the corona wirelengths 113A independently from that of the radius of the tubularcylinder electrode 104. By changing these two radii, both the coronadischarge electrode 102, which is an ionizer, and the precipitatingcylinder electrode 104 can be independently optimized, leading toimproved overall operation of the system.

[0073] The discs 108 and 110 are held together with a central support112. The fine wire 113 is threaded between the discs 108 and 110, andcarries the high voltage from the source 106. The high voltage again iscarried by wire through an insulator bushing 118, which is surrounded byhigh voltage carrying shield 120. An end plate 104A on tube 104 carriesthe voltages to the tube 104. The tube 104 in turn is connected to thedisc 108 for powering the corona discharge electrode 102. The flow ofgas is from an inlet 116 of housing 12 to an outlet 117, whichdischarges clean gas.

[0074]FIGS. 8 and 9 show a modified electrode design that can be usedwith the single-stage and the two-stage precipitators shown in FIGS. 1and 6. In this case, a plurality of support rods 120 are attached to thesupport discs 122 and 124 to form an assembly. A single corona fine wire126 is spirally wound around the support rods 120 to extend from onedisc to the other, and this forms a plurality of segments of conductivewire carrying current for supporting a corona discharge for chargingparticle in the droplet aerosol introduced through an inlet 128. Theporous media collector 129 is shown in FIG. 1 with a coarse filterformed at a bottom panel 130, and selected porosity on a cylindricalelectrically conductive porous side wall media 132. The cylindrical sidewall 132 acts to precipitate charged droplets and particles aspreviously shown. The cylindrical wall 132 is grounded, as is thehousing 12. An outlet 134 from the housing discharges clean gas. Theinsulator bushing 18, heater 22 and voltage source are the same as shownbefore.

[0075] The compact electrostatic precipitator described herein can beused to remove suspended particles in the blowby gas from a dieselengine or other internal combustion engines. The blowby gas with thesuspended particulate matter removed can be discharged directly into theatmosphere, or can be recirculated into the engine. FIGS. 10 and 11described below are both suitable for use for any electrostaticprecipitator, including that of the conventional design.

[0076]FIG. 10 shown one arrangement for blowby gas recirculation usingan electrostatic precipitator, preferably one made according to thepresent invention. The diesel engine 135 has a crankcase 136 and blowbygas from the engine crankcase 136 first flows along a passage through anelectrostatic precipitator 137 designed as show previously to removesuspended droplets or particles. The clean gas then flows into the inletsection of a T-connector 138 which has a orifice plate 138A in an outletsection. The gas flows through an orifice 140 in the plate 138A and intothe intake of a turbo charger 142. The side inlet section 136B of theT-connector 138 is open to atmosphere.

[0077] This T-connector constitutes a crankcase pressure regulatingdevice when an electrostatic precipitator is used to remove particlesfrom the blowby gas for recirculation into the diesel intake. Itsoperation is as follows. The T-connector 138 inlet 138B is open to theatmosphere, and thus the outlet of the precipitator 137 is also atatmospheric pressure. The crankcase pressure Pc relative to atmosphericpressure Pa is thus Pc−Pa=ΔP, where ΔP is the pressure drop of theblowby gas through the precipitator 137. This pressure drop is usuallyquite low, on the order of a few inches of water or less. The crankcasepressure is thus limited to a few inches of water above atmospheric. Inan internal combustion engine, the crankcase pressure must not beallowed to vary by more than a few inches above or below atmospheric toprevent leakage of crankcase oil to the outside, and other operationaldifficulties. This design makes it possible to achieve crankcasepressure regulation with a simple connection and at low cost.

[0078] In a diesel engine using a turbo-charger or turbo-compressor toincrease the engine power output, as shown in FIG. 10, a filter 144 isused at the air intake of the turbo-charger 142 to remove suspendedparticles in the ambient air. The pressure drop through the filter 144causes the pressure Pt at the turbocharger intake to be belowatmospheric. The diameter of the orifice 140 in the outlet section ofthe T-connector 138 is chosen such that the pressure drop across theorifice 140 (ΔP=Pa−Pt) is just sufficient to cause the gas flow throughthe orifice 140 to be the same as the blowby gas flow Q1 during normalengine operation, and when the engine intake air filter 144 is new. Whenthe intake filter 144 becomes partially clogged, its pressure dropincreases. This increases the gas flow through the orifice Q2. Thedifference, Q3=Q2−Q1 is made up by the air flow coming from the ambientthrough the side inlet section 138B of the T-connector 138.

[0079] Alternatively, as shown in FIG. 10A, a modified orifice housing139 can be made as a straight through flow tube with no side inlet foratmospheric air. An atmospheric inlet 139A can be connected to anopening in the diesel engine crankcase 136.

[0080] In both the arrangements shown in FIGS. 10 and 10A, the blowbygas passing through the electrostatic precipitator 137 is at arelatively high temperature. It also contains oil vapor which is notremoved by electrostatic precipitation. This oil vapor will condense onthe heat transfer surfaces of an intercooler 146 used at the outlet ofthe turbo-charger 142. Over time, the condensed oil will flood theintercooler 146 to cause a drop in the intercooler efficiency and thepower output of the diesel engine if not handled or removed.

[0081] To automatically remove this accumulated oil from the intercooler146, an oil sump 148 is provided in the intercooler to allow thecondensed oil to flow into the sump by gravity. The airflow from theintercooler 134 is directed through a flow restriction 150, such as anozzle or an orifice to create a pressure drop to remove the oil fromthe intercooler 146 and be carried by the airflow into the engineintake. The oil collected in the oil sump 148 can also be fed to theintake manifold 131 of the engine 135, by the back pressure created bythe flow restriction 150.

[0082]FIG. 11 shows a second arrangement for recirculating the blowbygas into a diesel engine 135. The crankcase 137 is connected to theelectrostatic precipitator 137 as before, but the T-connector 138 isremoved and the flow from the precipitator 137 is directed to a filterintake plenum 154 and allowed to pass through the filter 144 along withthe intake airflow. No crankcase pressure limiting arrangement is neededin this case. Since the precipitator outlet is always at atmosphericpressure, the crankcase pressure will thus be automatically limited tothat needed to maintain the blowby gas flow through the precipitator137.

[0083] When the hot blowby gas is directed this way into the filterintake 154, the oil vapor will be quickly cooled as it comes in contactwith the cool collecting filter elements of the filter 144. The vaporwill thus condense and be collected in the filter housing. At the sametime, all submicron size particles, which may not be completely removedby the electrostatic precipitator, will also be subjected to the strongthermophoretic forces created by the temperature gradient in theboundary layer of the gas flow around the collecting elements of thefilter 144. this thermophoretic force can be effectively utilized toremove these submicron particles. Normal engine intake air filters aredesigned to collect particles larger than a few micron in diameter only.Small particles in the submicron size range are usually not collected.By utilizing the thermophoretic force, the fine particles in the blowbygas can also be collected, thus making the incoming air to theturbo-charger cleaner. With proper design, oil and fine particleaccumulation in the intercooler can be reduced to very low level.

[0084]FIG. 12 is similar to FIG. 11 and the parts that are identical areidentically numbered. In FIG. 12 a controllable flow restrictor 158 isconnected to the outlet of the intercooler 146. The flow restrictor hasa retractable vane or blade 158A that can be introduced into theinterior passage of the restrictor and which is controlled by a solenoid159. The solenoid 159 is connected to the vane or blade 158A and willextend the blade into the flow passage when a signal is received by thesolenoid. An oil level sensor 160 is provided on the oil sump 148, andwhen the oil level in the sump reaches a set level, the signal isprovided to energize the solenoid 159. The vane or blade 158A is movedinto the flow passage in flow restrictor 158 to restrict flow throughthe outlet line.

[0085] This action increases the back pressure in the oil sump andforces the collected oil out a line 161 to the intake manifold 131 ofthe diesel engine. The solenoid controlled restrictor can be any desiredform, such a as a valve that closed partially, or an orifice that isintroduced into the flow passageway.

[0086]FIG. 13 is a sectional view of a modified version of typicalelectrode support 170. It can be molded from plastic and has an outerwall 172, with a plurality of projections or “prongs” shown at 174 whichmake the outer surface much like a serrated surface. A wire of suitablediameter indicated at 176 can be wound around the support 170 in ahelical fashion, much as shown in FIG. 8, with the points of theserrations or projections supporting the wire 176 at closely spacedintervals depending on the spacing of the serrations to insure that thewire 176 is maintained in a proper position relative to the collectorelectrode.

[0087]FIG. 14 is a vertical cross-sectional view of a modified form of acompact electrostatic precipitator 199. In this form of the invention, aconductive sleeve 200 forms a passage for fluid, with an inletconnection 202 for receiving an aerosol, and an outlet connection 203. Aflow passageway is defined by a plurality of openings 204 in a housingplate 206 that is supported on sleeve 206A, which is positioned at theupper end of the conductive sleeve 200, and is supported on a cap plate208 on a flange 210 formed on the end of the outer sleeve 200.

[0088] The support sleeve 206A has an open center, and an end insulatorportion 215 of a main electrode support 212 is mounted therein. Theupper end insulator portion 215 of the support 212 is supported on thecover 208 in a suitable manner. The upper end insulator portion has areceptacle for a heater assembly 216, which has heaters 218 mounted in aouter jacket 219 that is heat conducting and in contact with theinsulator portion 215. The outer jacket 219 can be made of copper, whichis a very good heat conductor, to distribute the heat uniformly to itsouter surface and keep the Insulator surface 213 hot and clean fromcontamination by vapor condensation and particle deposition. The topplate 220 is a heat insulator to reduce the heating power required tooperate the heater. The electrical power to operate the heater, usually12 or 24 volts, is carried by the electrical leads 221 passing throughthe top plate 220.

[0089] A power connection line 224 can be passed out through a centralopening of a cap 222. As shown, a power supply 226 to provide the highvoltage for the discharge electrode can be potted in the cap 222 and theconnector line or rod 225 can be within the precipitator and does nothave to extend through the cap. The line 224 can be a relatively lowvoltage, for example, a 24-volt supply could be provided. The heaters218 also would be connected generally to a 24-volt supply.

[0090] The main support 212 includes a hollow center electrode support214 that can be, for example, injection molded as a single piece withthe main support 212. The electrode support 214 has an interiorpassageway in which the high voltage connection rod or line electrode225 extends, and a thin electrode wire 227 can extend for connectiondirectly to the electrode wire shown at 228 that, as shown, is helicallywrapped around the insulating support 214. The electrode wire 228 isshown larger than actual size and is a thin wire as previouslyexplained. The insulating material sleeve 214 may be attached to themain support 212 with suitable screws threaded up into the support 212.The upper part of the insulating support has a conducting sleeve 217,which can be made of a metal and connected to the same high voltageelectrode wire 226. The insulating support 214 can have a cross sectionthat is cylindrical, if desired, or as shown in FIG. 15, it could berectangular with the outer collector electrode 200 also beingrectangular with care being taken so that at the corners there was auniform spacing between the wire 228 and the collector electrode.

[0091] The cross section can take any desired configuration, as long asthe spacings are maintained for a corona discharge.

[0092] The aerosol flow would come in as shown by the arrow 234, andflow up and around the passageway 235 between the high-voltage electrodewire 228 and the collector electrode 200. In this case, the collectorelectrode 200 is not a porous member, but is a solid member that caneither be stainless steel, for example, or could be a conductingplastic. As the flow passes through the space between the electrode wire228 and the collector 200, the particles are charged by the corona ionsproduced by the wire electrode 228. Some of these particles areprecipitated onto the collector 200 in this region. The remainingparticles are carried by the gas to the upper part of the assemblybetween the precipitator electrode 217 and the collector electrode 220,where they are precipitated onto the collector 220 by virtual of thehigh voltage on the electrode 217. The flow then goes up through theopenings 204, and out through the outlet 203 as shown. The main support212 and the electrode support 214 can be injection molded as a singlepiece, if desired., with conductors formed as slip-fit jackets, orwrapped wires. The heaters 218 are easily installed to maintain thetemperature of the insulator at a desired level.

[0093] The high temperature at the heaters keeps vapor that enters thespace between the sleeve 206A and the upper -high voltage insulatorportion 215 from condensing on the surface 213 of the high voltageinsulator portion 215 in the region around the center portion 215. Theheaters also provide enough heat to tend to repel contaminant particlesby the thermophoretic effect and prevent them from depositing on thesurface 213 of the high voltage insulator portion 215. The heaters 218are in heat transfer, contacting relation to the insulator portion 215and will maintain the temperature of the surface 213 sufficiently highto prevent contaminant particles from building up on the surface of theinsulator portion. Preferably the temperature of the surface 213 of theinsulator portion 215 is 10° or more than the temperature of the gas inthe vicinity of the insulating surface 213 inside the precipitatorhousing.

[0094]FIG. 16 is a transverse cross sectional view of a modifiedelectrode support 250 taken on the same line as FIG. 15. FIG. 17 is avertical cross sectional view of the modified electrode support 250. Awire 252 forming the electrode is in contact with the surface 254 of theelectrode support 250 and in substantial conformity to it. The wire 252can be wound around the support 250 as shown, and made to adhere to thesurface 254 by using a suitable adhesive material. When adhesives areused the wire 252 can have various patterns.

[0095] One such pattern for the wire 252 is shown in FIG. 18 at 258. InFIG. 18 a surface 262 of a support 260 has been unrolled to a flatsurface to review the wire pattern on the surface 262. The electricallyconductive discharge wire 264 is in contact with the support surface262, which is made of an electrically insulating material, such as aplastic or ceramic. The wire electrode 264 is of a substantially uniformdiameter and the distance between the wire segments and the adjacentcollector electrode is substantially uniform along the length of thewire. With a uniform distance between the wire 264 and the collectorelectrode, a substantially uniform corona discharge can be maintained.All parts of the wire 267 can thus be utilized effectively to insure ahigh charging efficiency in a small compact overall physical size forthe electrostatic droplet collector.

[0096] Another way of fabricating the thin wire discharge electrode isto use a flat, thin dielectric, generally plastic, having a thin filmclad on the outer surface. The flat thin dielectric with a thin film onthe outer surface can be similar to those used in fabricating flexible,electric circuit boards. The electrode wire pattern on the surface canbe etched by photolithography. The thin film forming the pattern canthen be applied to the surface of the support structure by an adhesive.In such a case, the wire will no longer have a circular cross section.The lateral dimension of the etched electrode, however, must besufficiently small to sustain a corona discharge at the applied highvoltage material.

[0097] The compact electrostatic precipitators shown are intendedprimarily for droplet aerosol collection. The high collection efficiencyfor the compact size also make the precipitators suitable for collectingdry particle aerosols. The collected dry particles will accumulate inthe unit and the precipitators must be periodically shut down forcleaning and maintenance. This is usually acceptable for mostapplications.

[0098] The compact electrostatic precipitator described herein, thoughnot necessary for the application, is particularly attractive because ofits compact physical size and high collection efficiency.

[0099] The invention as described above is for the preferredembodiments. Others, who are skilled in the art, will see otherpossibilities and embodiments to accomplish the same objectives based onthe principles and approaches described in the present specifications.

What is claimed is:
 1. An electrode assembly comprising a dischargeelectrode, an adjacent collector electrode, and a support structurehaving a longitudinal length and a transverse width, the dischargeelectrode comprising a thin wire supported on said structure with atotal length substantially longer than the length and the width, saidwire being substantially uniform in diameter, maintained atsubstantially the same distance from the adjacent collector electrode,and charged to a high voltage potential relative to said collector. 2.The electrode assembly of claim 1 , wherein said discharge electrodecomprises a plurality of thin wire segments supported on said structure.3. The electrode assembly of claim 2 , wherein said wire segmentscomprise substantially parallel lengths of wires with adjacent wiresegments spaced from each other at a substantially uniform distance. 4.The electrode assembly of claim 2 , wherein the wire segments extend ina generally longitudinal direction.
 5. The electrode assembly of claim 2, wherein said wire segments extend in a generally transverse directionand substantially perpendicular to the longitudinal length.
 6. Theelectrode assembly of claim 2 , wherein the wire segments extend in agenerally spiral pattern along the longitudinal length.
 7. The electrodeassembly of claim 2 , wherein the ratio SID is kept within the range of0.1 to 10, where S is the spacing between the adjacent wire segments andD is the distance between the wire segment and the nearest point on theadjacent collector electrode surface.
 8. The electrode assembly of claim1 , and further including a precipitator electrode, said precipitatorelectrode having a conducting surface substantially parallel to saidcollector electrode and maintained at substantially the same highvoltage potential relative to said collector electrode as the dischargeelectrode.
 9. The electrode assembly of claim 1 , wherein the collectorelectrode and the support structure for the discharge electrode are of agenerally cylindrical shape.
 10. The electrode assembly of claim 1 ,wherein the collector electrode and the support structure for thedischarge electrode are of a generally rectangular shape.
 11. Anelectrode assembly of claim 1 , wherein the support structure for thedischarge electrode comprises a conducting material.
 12. An electrodeassembly of claim 1 , wherein the support structure for the dischargeelectrode comprises an insulating material.
 13. An electrode assembly ofclaim 1 , wherein said support structure for the discharge electrode hasan insulating surface.
 14. An electrode assembly of claim 13 , whereinsaid wire is supported on the structure in substantial conformity to thesurface of the support.
 15. An electrode assembly of claim 1 , whereinthe collector electrode comprises a porous conducting material.
 16. Anelectrostatic precipitator in combination with a diesel engine havingcrankcase blowby, and a connection to carry a flow of the blowby gasthrough the electrostatic precipitator for removing suspendedparticulate matter from the blowby gas, said electrostatic precipitatorcomprising a discharge electrode, an adjacent collector electrode, ahousing containing the electrodes, an insulator, a conductor passingthrough said insulator and carrying the high voltage to the dischargeelectrode inside said housing, and a heater, said housing being capableof carrying a gas from an inlet to an outlet, said insulator having anexternal surface in contact with gas inside said housing, and saidinsulator being in contact with said heater to maintain a surfacetemperature sufficiently high to prevent contaminant buildup on saidinsulator surface.
 17. The electrostatic precipitator of claim 16 ,wherein the surface temperature of the insulator is maintained at 10° C.or more above the temperature of gas in contact with the insulatorinside said electrostatic precipitator housing.
 18. The electrostaticprecipitator of claim 16 , wherein said insulator being at leastpartially surrounded by a conductive shield, said shield being held at avoltage substantially the same as the voltage on the collectorelectrode.
 19. An electrostatic precipitator comprising the electrodeassembly of claim 1 in combination with a housing capable of carrying agas from an inlet to an outlet, the electrode assembly being supportedin said housing.
 20. The electrostatic precipitator of claim 19 incombination with a diesel engine having crankcase blowby, and aconnection to carry a flow of the blowby gas through the electrostaticprecipitator for removing suspended particulate matter from the blowbygas.
 21. The combination of claim 20 , wherein the housing outlet iscoupled to an inlet to the diesel engine.
 22. An electrostaticprecipitator comprising a housing capable of carrying a gas from aninlet to an outlet; a discharge electrode assembly supported in saidhousing; a collector electrode comprising a porous conductive mediumsurrounding said discharge electrode; and a droplet containing gas flowentering the inlet and flowing toward the discharge electrode, throughthe surrounding collector electrode, and out the outlet of the housing,said discharge electrode being maintained at a high voltage potentialrelative to the collector electrode to provide a charge to particles inthe gas flow that are collected on the collector electrode.
 23. Theelectrostatic precipitator of claim 22 and a precipitator electrodehaving a conductive surface substantially parallel to the collectorelectrode, said precipitator electrode being maintained at substantiallythe same high voltage potential relative to the collector electrode asthe discharge electrode.
 24. An electrostatic precipitator comprising ahousing capable of carrying a gas from an inlet to an outlet, adischarge electrode assembly and a collector electrode supported in saidhousing, and a droplet containing gas flow entering the inlet, saiddischarge electrode being maintained at a high voltage potentialrelative to the collector electrode to provide a charge to particles inthe gas flow that are collected on the collector electrode.
 25. Acrankcase pressure regulator for blowby gas recirculation through anelectrostatic precipitator for a diesel engine comprising an inlet, anoutlet, a flow restriction between the inlet and outlet, and anatmospheric air opening providing atmospheric air through the flowrestriction, said inlet being connected to the electrostaticprecipitator, and said outlet being connected to an inlet of the dieselengine.
 26. The crankcase pressure regulator of claim 25 , wherein thesaid atmospheric air opening is between an inlet of said flowrestriction and the outlet of said electrostatic precipitator.
 27. Thecrankcase pressure regulator of claim 25 , wherein the said atmosphericair inlet comprises an opening in the crankcase of said diesel engine.28. An automatic condensed oil remover for an intercooler of a dieselengine comprising a flow restrictor between the intercooler and thediesel engine, an oil sump in the intercooler, and an oil tube to carrycondensed oil from the oil sump to the diesel engine.
 29. The condensedoil remover of claim 28 , wherein the flow restrictor is selectivelyoperated to create pressure drop sufficient to force the oil to flowfrom the oil sump through the oil tube to the diesel engine, and acontrol to selectively operate the flow restrictor.
 30. An automaticcondensed oil removal system comprising the condensed oil system ofclaim 28 , and an oil level sensor to provide the signal to actuate theflow restrictor and create a pressure drop sufficient to force the oilto flow from the oil sump through the oil tube to the diesel engine. 31.A crankcase blowby gas recirculation system for diesel enginescomprising an electrostatic precipitator with an inlet coupled to thecrankcase and an outlet coupled to the intake side of the engine intakeair filter.